Weak localization in twisted double bilayer graphene

Stacking two Bernal-stacked bilayer graphene sheet together with a twist angle θ makes a twisted double bilayer graphene (tDBG); adding top and back gates enables the Moire-modified band structure to be tuned independent of the filling of those bands. In tDBG devices with θ~1.2-1.3°, the first Moire conduction band is nearly flat and isolated fron neighboring bands over a narrow range of perpendicular displacement field, where correlated insulator and correlated metallic phases appear and where spin and/or valley symmetries are believed to be broken. Here, we present an investigation of low field magnetoresistance on tDBG devices down to 20mK. The data display a weak localization (WL) correction throughout most of the correlated metal phase, mapping out regions in which time reversal symmetry is intact; outside of the correlated metal phase, the WL correction is rarely seen. Modifications to the WL correction due to proximal WSe₂ will also be discussed.